1. Technical Field
The present invention relates to a lighting device and an optical apparatus using a laser beam source.
2. Related Art
An endoscope device which uses a laser beam source for illumination is known. Since energy of laser beam concentrates on an extremely limited area, some technique is required for using the laser beam source as a source for emitting illumination light sufficient for uniformly illuminating a region having a certain area such as a portion of physical change caused by disease. According to a technique disclosed in JP-A-8-224208, for example, laser beam is bended by using a concave lens 11 provided at a distal end of an endoscope so as to obtain uniform illumination for a physically changed portion by disease.
Since energy of laser beam concentrates on an extremely limited area, the concave lens included in the above technique for decreasing the concentration needs to have an extremely acute angle from the center toward the peripheral area. In this case, laser beam having high energy density is applied when the center of the laser beam shifts from the center of the concave lens even slightly. As a result, light points having high luminance appear on the radiation area, and therefore uniform illumination cannot be acquired.
According to the structure of the endoscope, optical fibers are provided between the light source and the distal end portion. The endoscope distal end portion is inserted toward the physically changed area by disease by freely bending the regions of the optical fibers. In this case, it is difficult to precisely match the center of the optical element such as the concave lens disposed at the distal end of the endoscope with the center of the laser beam positioned at the other end. Thus, uniform illumination sufficient for the endoscope is difficult to obtain by using the technology disclosed in the above reference.
These problems arise not only from the case of the endoscope but also from a wide variety of cases where precise determination of relative positions of an optical element for equalizing light and a light source device is difficult under the condition of illumination constituted by light having high energy density.